Brain Tumor Accumulation Research Articles

Blood-brain barrier and blood-brain tumor barrier penetrating peptide-drug conjugate as targeted therapy for the treatment of lung cancer brain metastasis

Lung cancer is the leading cause of cancer deaths worldwide. Brain metastasis of lung cancer, which counts for nearly 50% of late-stage lung cancer patients, is a sign of a really poor prognosis. However, the presence of blood–brain barrier (BBB) and blood–brain tumor barrier (BBTB) limits the penetration of drugs from the blood into the brain and thus restricts their accumulation in brain tumors. Systematic delivery of drugs into brain and brain tumor lesion using BBB and BBTB penetrating vehicles represents a promising strategy to overcome the BBB and BBTB limitations. Hence, we validated one of our previously identified BBB/BBTB penetrating peptide and its drug conjugate form for the treatment of lung cancer brain metastasis. With in vitro experiment, we first validated that the receptor LRP1, which mediated the peptide penetration of the BBB, was expressed on lung cancer cells and thus can be targeted by the peptide to overcome BBTB. With this delivery peptide, we constructed peptide-paclitaxel conjugate (the PDC) and in vitro validation showed that the PDC can across the BBB and efficiently kill lung cancer cells. We therefore constructed mouse lung cancer brain metastasis xenograft. In vivo anti-tumor validations showed that the PDC efficiently inhibited the proliferation of the brain resident lung cancer cells and significantly expanded the survival of the mouse xenograft, with no visible damages to the organs. Overall, our study provided potential therapeutic drugs for the treatment of lung cancer brain metastasis that may be clinically effective in the near future.

Ultrasound frequency-controlled microbubble dynamics in brain vessels regulate the enrichment of inflammatory pathways in the blood-brain barrier

Microbubble-enhanced ultrasound provides a noninvasive physical method to locally overcome major obstacles to the accumulation of blood-borne therapeutics in the brain, posed by the blood-brain barrier (BBB). However, due to the highly nonlinear and coupled behavior of microbubble dynamics in brain vessels, the impact of microbubble resonant effects on BBB signaling and function remains undefined. Here, combined theoretical and prospective experimental investigations reveal that microbubble resonant effects in brain capillaries can control the enrichment of inflammatory pathways that are sensitive to wall shear stress and promote differential expression of a range of transcripts in the BBB, supporting the notion that microbubble dynamics exerted mechanical stress can be used to establish molecular, in addition to spatial, therapeutic windows to target brain diseases. Consistent with these findings, a robust increase in cytotoxic T-cell accumulation in brain tumors was observed, demonstrating the functional relevance and potential clinical significance of the observed immuno-mechano-biological responses.

Brain-Targeted Cas12a Ribonucleoprotein Nanocapsules Enable Synergetic Gene Co-Editing Leading to Potent Inhibition of Orthotopic Glioblastoma.

Gene-editing technology shows great potential in glioblastoma (GBM) therapy. Due to the complexity of GBM pathogenesis, a single gene-editing-based therapy is unlikely to be successful; therefore, a multi-gene knockout strategy is preferred for effective GBM inhibition. Here, a non-invasive, biodegradable brain-targeted CRISPR/Cas12a nanocapsule is used that simultaneously targeted dual oncogenes, EGFR and PLK1, for effective GBM therapy. This cargo nanoencapsulation technology enables the CRISPR/Cas12a system to achieve extended blood half-life, efficient blood-brain barrier (BBB) penetration, active tumor targeting, and selective release. In U87MG cells, the combinatorial gene editing system resulted in 61% and 33% knockout of EGFR and PLK1, respectively. Following systemic administration, the CRISPR/Cas12a system demonstrated promising brain tumor accumulation that led to extensive EGFR and PLK1 gene editing in both U87MG and patient-derived GSC xenograft mouse models with negligible off-target gene editing detected through NGS. Additionally, CRISPR/Cas12a nanocapsules that concurrently targeted the EGFR and PLK1 oncogenes showed superior tumor growth suppression and significantly improved the median survival time relative to nanocapsules containing single oncogene knockouts, signifying the potency of the multi-oncogene targeting strategy. The findings indicate that utilization of the CRISPR/Cas12a combinatorial gene editing technique presents a practical option for gene therapy in GBM.

Size-Dependent Glioblastoma Targeting by Polymeric Nanoruler with Prolonged Blood Circulation.

Currently, there is no effective treatment for glioblastoma multiforme (GBM), the most frequent and malignant type of brain tumor. The blood-brain (tumor) barrier (BB(T)B), which is composed of tightly connected endothelial cells and pericytes (with partial vasculature collapse), hampers nanomedicine accumulation in tumor tissues. We aimed to explore the effect of nanomedicine size on passive targeting of GBM. A series of size-tunable poly(ethylene glycol) (PEG)-grafted copolymers (gPEGs) were constructed with hydrodynamic diameters of 8-30 nm. Biodistribution studies using orthotopic brain tumor-bearing mice revealed that gPEG brain tumor accumulation was maximized at 10 nm with ∼14 dose %/g of tumor, which was 19 times higher than that in the normal brain region and 4.2 times higher than that of 30-nm gPEG. Notably, 10-nm gPEG exhibited substantially higher brain tumor accumulation than 11-nm linear PEG owing to the prolonged blood circulation property of gPEGs, which is derived from a densely PEG-packed structure. 10 nm gPEG exhibited deeper penetration into the brain tumor tissue than the larger gPEGs did (>10 nm). This study demonstrates, for the first time, the great potential of a nanomedicine downsizing strategy for passive GBM targeting.

A Novel ANG-BSA/BCNU/ICG MNPs Integrated for Targeting Therapy of Glioblastoma.

Develop an albumin nanoparticle-based nanoprobe for targeted glioblastoma (GBM) diagnosis and treatment, utilizing Angopep-2 for low-density lipoprotein receptor-related protein (LRP) targeting. Combined albumin-coated superparamagnetic iron oxide (SPIO), Carmustine (BCNU), and indocyanine green (ICG). Assessed morphology, size, Zeta potential, fluorescence, and drug encapsulation. Conducted in vitro fluorescence/MRI imaging and cell viability assays, and in vivo nanoprobe accumulation evaluation in brain tumors. ANG-BSA/BCNU/ICG MNPs exhibited superior targeting and cytotoxicity against GBM cells in vitro. In vivo, enhanced brain tumor accumulation during imaging was observed. This targeted imaging and drug delivery system holds promise for efficient GBM therapy and intraoperative localization, addressing Blood-brain barrier (BBB) limitations with precise drug delivery and imaging capabilities.

Tuning the Elasticity of Polymersomes for Brain Tumor Targeting.

Nanoformulations show great potential for delivering drugs to treat brain tumors. However, how the mechanical properties of nanoformulations affect their ultimate brain destination is still unknown. Here, a library of membrane‐crosslinked polymersomes with different elasticity are synthesized to investigate their ability to effectively target brain tumors. Crosslinked polymersomes with identical particle size, zeta potential and shape are assessed, but their elasticity is varied depending on the rigidity of incorporated crosslinkers. Benzyl and oxyethylene containing crosslinkers demonstrate higher and lower Young's modulus, respectively. Interestingly, stiff polymersomes exert superior brain tumor cell uptake, excellent in vitro blood brain barrier (BBB) and tumor penetration but relatively shorter blood circulation time than their soft counterparts. These results together affect the in vivo performance for which rigid polymersomes exerting higher brain tumor accumulation in an orthotopic glioblastoma (GBM) tumor model. The results demonstrate the crucial role of nanoformulation elasticity for brain‐tumor targeting and will be useful for the design of future brain targeting drug delivery systems for the treatment of brain disease.

Croconaine-based nanoparticles enable efficient optoacoustic imaging of murine brain tumors

Contrast enhancement in optoacoustic (photoacoustic) imaging can be achieved with agents that exhibit high absorption cross-sections, high photostability, low quantum yield, low toxicity, and preferential bio-distribution and clearance profiles. Based on advantageous photophysical properties of croconaine dyes, we explored croconaine-based nanoparticles (CR780RGD-NPs) as highly efficient contrast agents for targeted optoacoustic imaging of challenging preclinical tumor targets. Initial characterization of the CR780 dye was followed by modifications using polyethylene glycol and the cancer-targeting c(RGDyC) peptide, resulting in self-assembled ultrasmall particles with long circulation time and active tumor targeting. Preferential bio-distribution was demonstrated in orthotopic mouse brain tumor models by multispectral optoacoustic tomography (MSOT) imaging and histological analysis. Our findings showcase particle accumulation in brain tumors with sustainable strong optoacoustic signals and minimal toxic side effects. This work points to CR780RGD-NPs as a promising optoacoustic contrast agent for potential use in the diagnosis and image-guided resection of brain tumors.

Angiopep-2 Modified Cationic Lipid-Poly-Lactic-Co-Glycolic Acid Delivery Temozolomide and DNA Repair Inhibitor Dbait to Achieve Synergetic Chemo-Radiotherapy Against Glioma.

The therapeutic treatment of glioblastoma multiforme (GBM) remains a major challenge. Synergistic chemotherapy and radiotherapy (RT) have been considered the standard clinical therapy for malignant glioma, but there are some outstanding problems. First, gliomas are deemed exceedingly radio-resistant tumors, owing to efficient DNA double-strand break repair. In addition, the first-line chemotherapeutic agent (temozolomide, TMZ) for glioma shows extensive side effects and low accumulation in brain tumors. Therefore, we designed and constructed an Angiopep-2 modified cationic lipid-Poly-lactic-co-glycolic acid (PLGA), Angiopep-2 (A2)/DSPE-PEG2000/DOTAP/PLGA (APDP), to transport TMZ and a DNA repair inhibitor (Dbait) into glioblastoma cells, achieving concomitant chemo-radiotherapy treatment of glioma. At the cellular level, the APDP+TMZ/Dbait can be well endocytosed and enhance accumulation of the agent in brain tumors. Furthermore, the nanoparticle combined with Dbait improves the efficiency of radiotherapy in GBM. Our experimental data demonstrate that APDP+TMZ/Dbait has great potential as a multipurpose nanomedicine for the synergistic chemo-radiotherapy and radio-sensitization of malignant glioma in precise medical applications.

CEST MRI of 3-O-methyl-D-glucose uptake and accumulation in brain tumors.

3-O-Methyl-D-glucose (3-OMG) is a nonmetabolizable structural analog of glucose that offers potential to be used as a CEST-contrast agent for tumor detection. Here, we explore it for CEST-detection of malignant brain tumors and compare it with D-glucose. Glioma xenografts of a U87-MG cell line were implanted in five mice. Dynamic 3-OMG weighted images were collected using CEST-MRI at 11.7T at a single offset of 1.2 ppm, showing the effect of accumulation of the contrast agent in the tumor, following an intravenous injection of 3-OMG (3g/kg). Tumor regions showed higher enhancement as compared to contralateral brain. The CEST contrast enhancement in the tumor region ranged from 2.5-5.0%, while it was 1.5-3.5% in contralateral brain. Previous D-glucose studies of the same tumor model showed an enhancement of 1.5-3.0% and 0.5-1.5% in tumor and contralateral brain, respectively. The signal gradually stabilized to a value that persisted for the length of the scan. 3-OMG shows a CEST contrast enhancement that is approximately twice as much as that of D-glucose for a similar tumor line. In view of its suggested low toxicity and transport properties across the BBB, 3-OMG provides an option to be used as a nonmetallic contrast agent for evaluating brain tumors.

IRGD-mediated core-shell nanoparticles loading carmustine and O6-benzylguanine for glioma therapy

iRGD (internalizing RGD) with high affinity to αν integrins was reported to enhance tumor penetrability by binding to neuropilin-1 (NRP-1). Based on our previous study, chitosan surface-modified poly (lactide-co-glycolides) nanoparticles (PLGA/CS NPs), loaded with carmustine (BCNU) and its sensitizer (O6-benzylguanine, BG) showed stronger anti-tumor effect than free drugs. In present study, PLGA/CS NPs (NPs) with core-shell structure were prepared and modified with iRGD or mPEG. F98, C6 or U87 cell lines with different receptors levels were selected for in vitro and in vivo studies. After administration of iRGD-mediated NPs, including iRGD-modified NPs (iRGD-NPs) and co-administration of iRGD and NPs (iRGD + NPs), their effects on glioma were compared with NPs. iRGD-NPs showed stronger cytotoxicity and cellular uptake than other groups. iRGD-NPs and iRGD + NPs displayed deeper tumor penetration and stronger anti-invasion effect on three dimensional (3D) glioma spheroids than NPs. On F98 glioma-bearing mice model, iRGD-mediated NPs showed enhanced crossing BBB ability and brain tumor accumulation levels. Correspondingly, the median survival time of iRGD + NPs, iRGD-NPs and NPs groups were 58, 49 and 34.5 days, respectively. Present studies supported the iRGD-mediated strategy to improve the efficacy of antitumor drug delivery system. Importantly, co-administration of iRGD may be a greater way over the conjugation of iRGD.

Optical imaging of targeted β-galactosidase in brain tumors to detect EGFR levels.

A current limitation in molecular imaging is that it often requires genetic manipulation of cancer cells for noninvasive imaging. Other methods to detect tumor cells in vivo using exogenously delivered and functionally active reporters, such as β-gal, are required. We report the development of a platform system for linking β-gal to any number of different ligands or antibodies for in vivo targeting to tissue or cells, without the requirement for genetic engineering of the target cells prior to imaging. Our studies demonstrate significant uptake in vitro and in vivo of an EGFR-targeted β-gal complex. We were then able to image orthotopic brain tumor accumulation and localization of the targeted enzyme when a fluorophore was added to the complex, as well as validate the internalization of the intravenously administered β-gal reporter complex ex vivo. After fluorescence imaging localized the β-gal complexes to the brain tumor, we topically applied a bioluminescent β-gal substrate to serial sections of the brain to evaluate the delivery and integrity of the enzyme. Finally, robust bioluminescence of the EGFR-targeted β-gal complex was captured within the tumor during noninvasive in vivo imaging.

Preclinical Pharmacological Evaluation of a Novel Multiple Kinase Inhibitor, ON123300, in Brain Tumor Models

ON123300 is a low molecular weight multikinase inhibitor identified through a series of screens that supported further analyses for brain tumor chemotherapy. Biochemical assays indicated that ON123300 was a strong inhibitor of Ark5 and CDK4, as well as growth factor receptor tyrosine kinases such as β-type platelet-derived growth factor receptor (PDGFRβ). ON123300 inhibited U87 glioma cell proliferation with an IC(50) 3.4 ± 0.1 μmol/L and reduced phosphorylation of Akt, yet it also unexpectedly induced Erk activation, both in a dose- and time-dependent manner that subsequently was attributed to relieving Akt-mediated C-Raf S259 inactivation and activating a p70S6K-initiated PI3K-negative feedback loop. Cotreatment with the EGFR inhibitor gefitinib produced synergistic cytotoxic effects. Pursuant to the in vitro studies, in vivo pharmacokinetic and pharmacodynamic studies of ON123300 were completed in mice bearing intracerebral U87 tumors following intravenous doses of 5 and 25 mg/kg alone, and also at the higher dose concurrently with gefitinib. ON123300 showed high brain and brain tumor accumulation based on brain partition coefficient values of at least 2.5. Consistent with the in vitro studies, single agent ON123300 caused a dose-dependent suppression of phosphorylation of Akt as well as activation of Erk in brain tumors, whereas addition of gefitinib to the ON123300 regimen significantly enhanced p-Akt inhibition and prevented Erk activation. In summary, ON123300 demonstrated favorable pharmacokinetic characteristics, and future development for brain tumor therapy would require use of combinations, such as gefitinib, that mitigate its Erk activation and enhance its activity.

Abstract 2449: Molecular imaging of the cancer signature using targeted-split enzyme complementation

Abstract Noninvasive diagnosis of any disease is a crucial step in the prevention, treatment and reduction of the mortality rate. Further, tailoring clinical diagnostics and therapeutics to specific forms of cancer and even to the precise aberrant biological events underlying cancer development in a particular patient has focused significant research on molecular signatures. For instance, cell surface receptors important in tumorigenesis are expressed at different levels during the multistage process and are routinely used to guide treatment regimes. Moreover, mutational events that drive a normal cell to become a cancer cell require the coordinated overexpression of not just one receptor at a time, but rather multiple biomarkers. Many cancers, including gliomas, are characterized by an abnormal increase in the activity of epidermal growth factor receptors (EGFR) and transferrin receptors (TfR). Our data of representative human cancer cell lines demonstrate unique, observable expression patterns for the two receptors. Current diagnostic techniques such as medical imaging, tissue biopsy, and bioanalytical assay of body fluids are relatively insensitive and lack the specificity to detect these physiologic changes simultaneously. To develop imaging tools that take advantage of the molecular signature, new technologies must employ an activity-based imaging agent conjugated to a targeting element. By linking a reporter enzyme, such as α-gal, to a targeting moiety, either ligand or a short peptide, signal-amplification at the molecular level is achieved. We divided α-gal into unique, independent polypeptides that reassemble and complement enzymatic activity in bacteria and in mammalian cells. We created two sets of complementing pairs that individually have no enzymatic activity. However, when brought into close proximity, complementing pairs associate, resulting in detectable enzymatic activity. We then constructed a targeting complex composed of reporter fragment, linker, and targeting moiety. Our studies demonstrate a time course- and dose-dependent uptake in vitro. Further, we were able to simultaneously visualize the two cell surface receptors implicated in gliomas, EGFR and TfR, using complementing pairs of the targeted-reporter fragment complex. In addition, we were able to image orthotopic brain tumor accumulation and localization of the targeted-enzyme when a fluorescence reporter was added to the complex, as well as immunohistochemical staining of the α-gal reporter complex ex vivo. After fluorescence imaging localized the α-gal complexes to the brain tumor, we topically applied a bioluminescent α-gal substrate to serial sections of the brain to evaluate the delivery and integrity of enzyme. Robust bioluminescence was captured within the tumor after 3 min, indicating that α-gal maintained its activity. Current experiments are underway to image the enzyme complementation noninvasively in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2449. doi:1538-7445.AM2012-2449

Abstract 1407A: Imaging the coordinated expression of cell surface receptors in gliomas using a novel multi-functional enzyme reporter complementation complex

Abstract Diagnosis of any disease is crucial in the prevention, treatment and reduction of the mortality rate. Tailoring clinical diagnostics and therapeutics to specific forms of cancer and even to the precise aberrant biological events underlying cancer development in a particular patient has focused significant research on molecular signatures. For instance, cell surface receptors important in tumorigenesis are expressed at different levels during the multi-stage process and are routinely used to guide treatment regimes. Mutational events that drive a normal cell to become a cancer cell require the coordinated overexpression of not just one receptor at a time, but rather multiple biomarkers. Many cancers are characterized by an abnormal increase in the activity of epidermal growth factor receptors (EGFR) and transferrin receptors (TfR). Our data of representative human cancer cell lines demonstrate unique, observable expression patterns for the two receptors. Current diagnostic techniques such as medical imaging, tissue biopsy, and bio-analytical assay of body fluids are relatively insensitive and lack the specificity to detect these physiologic changes simultaneously. To develop imaging tools that take advantage of the molecular signature, new technologies must employ a contrast agent or signal-amplifying material conjugated to a targeting agent. By linking a reporter enzyme, such as β-gal, to a targeting moiety, signal-amplification at the molecular level is achieved. We divided β-gal into unique, independent polypeptides that reassemble and complement enzymatic activity in bacteria and in mammalian cells. We created two sets of complementing pairs that individually have no enzymatic activity. However, when brought into close proximity, complementing pairs associate, resulting in detectable enzymatic activity. We then constructed a targeting complex composed of reporter fragment, linker, and targeting moiety. Our studies demonstrate a time course- and dose-dependent uptake in vitro. Further, we were able to simultaneously visualize the two cell surface receptors implicated in gliomas, EGFR and TfR, using complementing pairs of the targeted-reporter fragment complex. In addition, we were able to image orthotopic brain tumor accumulation and localization of the targeted-complexes when a fluorescence reporter was added to the complex, as well as immunohistochemical staining of the β-gal reporter complex ex vivo. After fluorescence imaging localized the β-gal complexes to the brain tumor, we topically applied a bioluminescent β-gal substrate to serial sections of the brain to evaluate the delivery and integrity of enzyme. Robust bioluminescence was captured within the tumor after 3 min, indicating that β-gal maintained its activity. Current experiments are underway to image the enzyme complementation non-invasively. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1407A. doi:10.1158/1538-7445.AM2011-1407A

A novel mutual prodrug-induced, and quantitatively and selectively enhanced PpIX accumulation in brain tumors

A novel mutual prodrug-induced, and quantitatively and selectively enhanced PpIX accumulation in brain tumors

Inhibition of brain tumor growth by intravenous poly(β- l -malic acid) nanobioconjugate with pH-dependent drug release

Effective treatment of brain neurological disorders such as Alzheimer's disease, multiple sclerosis, or tumors should be possible with drug delivery through blood-brain barrier (BBB) or blood-brain tumor barrier (BTB) and targeting specific types of brain cells with drug release into the cell cytoplasm. A polymeric nanobioconjugate drug based on biodegradable, nontoxic, and nonimmunogenic polymalic acid as a universal delivery nanoplatform was used for design and synthesis of nanomedicine drug for i.v. treatment of brain tumors. The polymeric drug passes through the BTB and tumor cell membrane using tandem monoclonal antibodies targeting the BTB and tumor cells. The next step for polymeric drug action was inhibition of tumor angiogenesis by specifically blocking the synthesis of a tumor neovascular trimer protein, laminin-411, by attached antisense oligonucleotides (AONs). The AONs were released into the target cell cytoplasm via pH-activated trileucine, an endosomal escape moiety. Drug delivery to the brain tumor and the release mechanism were both studied for this nanobiopolymer. Introduction of a trileucine endosome escape unit resulted in significantly increased AON delivery to tumor cells, inhibition of laminin-411 synthesis in vitro and in vivo, specific accumulation in brain tumors, and suppression of intracranial glioma growth compared with pH-independent leucine ester. The availability of a systemically active polymeric drug delivery system that passes through the BTB, targets tumor cells, and inhibits glioma growth gives hope for a successful strategy of glioma treatment. This delivery system with drug release into the brain-specific cell type could be useful for treatment of various brain pathologies.

Abstract 3702: Novel nanoparticle-delivered compound, Imipramine Blue, halts glioma invasion by affecting actin dynamics

Abstract Statement of Purpose: Due to their invasive nature, malignant gliomas are difficult neoplasms to treat leading to poor prognosis. Invasive gliomas therefore elude current treatment involving chemotherapy, surgical resection and radiation. Additionally, anti-angiogenic therapy often enhances invasion and current ‘anti-invasive’ agents fail clinically. Here, we identify a new anti-invasive compound and target it therapeutically to invasive brain tumors. Methods: Twenty-four small molecule compounds designed to have novel anti-tumor effects via NADPH oxidase inhibition were screened for anti-invasive properties against the rat glioma model RT2 using modified Boyden chamber assay. One compound, Imipramine Blue(IB), was identified to be anti-invasive but not cytotoxic. IB was encapsulated using liposomes (Nano-IB) to improve its pharmacokinetics and increase its preferential accumulation in brain tumors. Rats inoculated with RT2 invasive glioma were treated with either saline or nano-IB (3mg/kg total) on day 4 and 7 after orthotopic tumor inoculation, and sacrificed via intracardial perfusion on day 11. One set of animals was prepared for histological examination and another for and RNA (n=3 per group) and protein (n=3 per group) harvest. Microarray analysis was performed using the Affymetrix 230 2.0 system at Morehouse School of Medicine (Atlanta, GA) and analyzed using Genespring and Ingenuity Pathway Analysis (IPA). Confirmatory quantitative rt-PCR and Western blotting were performed for genes of interest. Results: When delivered in vivo, Nano-IB halted invasion as determined by analyzing tumor borders on day 11 by imaging analysis. Microarray analysis indicated greater than 2-fold change in approximately 60 genes including, a subset of genes involved in the regulation of actin polymerization: scinderin, profilin-1, calgranulin, α-actin, and rhoGTPase inhibitor A. Confirmatory rt-PCR using pooled RNA samples and western blotting confirmed the differences seen in microarray. Using IPA, several upstream candidate target molecules were identified which may be acting to cause the downstream effects including PI3K, PKC, and MAPK/ERK. Further, using IB in vitro showed dramatic effects on the actin cytoskeleton in the RT2 cells. Conclusions: Imipramine Blue, a novel small molecule therapeutic, effectively halts invasion of the RT2 astrocytoma cell line in vitro and in vivo as evidenced by Boyden chamber assay and histological examination brain inoculated with invasive RT-2 tumors. Furthermore, the drug is acting via alteration of the actin cytoskeleton as shown in vitro by cytological examination and in vivo through microarray and western blotting analysis. However, due to number of genes that are affected upon treatment the drug is not directly acting on actin filaments in the cell but rather on an upstream regulator of actin polymerization regulating molecules. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3702.

Predicting Human Tumor Drug Concentrations from a Preclinical Pharmacokinetic Model of Temozolomide Brain Disposition

Knowledge of drug concentrations in tumors is critical for understanding the determinants of drug accumulation in tumors. Because significant obstacles prevent making these measurements in humans, development of a predictive pharmacokinetic model would be of great value to the translation of preclinical data to the clinic. Our goal was to show how the latter could be achieved for temozolomide, an agent used in the treatment of brain tumors, using an orthotopic brain tumor model in rats. Rats bearing i.c. tumors received 20 mg/kg i.v. of temozolomide followed by the subsequent measurement of serial plasma, cerebrospinal fluid (CSF), normal brain, and brain tumor temozolomide concentrations. The resultant data provided the framework to develop a hybrid physiologically based pharmacokinetic model for temozolomide in brain. The preclinical pharmacokinetic model was scaled to predict temozolomide concentrations in human CSF, normal brain, and brain tumor, and through a series of Monte Carlo simulations, the accumulation of temozolomide in brain tumors under conditions of altered blood-brain barrier permeability, fractional blood volume, and clinical dosing schedules was evaluated. The developed physiologically based pharmacokinetic model afforded a mechanistic and accurate prediction of temozolomide brain disposition in rats, which through model scale-up procedures accurately predicted the CSF/plasma area under the drug concentration-time curve ratios of 0.2 reported in patients. Through a series of model simulations, it was shown that the brain tumor accumulation of temozolomide varied substantially based on changes in blood-brain barrier permeability and fractional tumor blood volume but minimally based on clinical dosing regimens. A physiologically based pharmacokinetic modeling approach offers a means to translate preclinical to clinical characteristics of drug disposition in target tissues and, thus, a means to select appropriate drug dosing regimens for achieving optimal target tissue drug concentrations.

Lipids in brain tumors.

ELATIVELY few studies have been performed on lipids of brain tumors. The pioneer study of Brante ~ showed that brain tumors in general have a lipid content lower than normal brain and contain esterified cholesterol, which is absent from normal adult brain tissue. Phospholipids are also present in small amounts/The presence in brain tumors of free fatty acids, triglycerides, and cholesterol esters, and certain lipids absent from normal brain, has been detected in our laboratory/Azarnoff and coworkers t demonstrated that human glioblastomas, astrocytomas, and other intracranial tumors are capable of incorporating 14C-acetate into cholesterol in contrast with normal brain tissue which is known to synthesize cholesterol only to a limited extent. Paoletti, et al./ demonstrated that the Zimmerman ependymoma can convert various precursors into cholesterol much more efficiently than normal brain of the same animals. A typical feature of brain tumors is the presence of desmosterol (24-dehydrocholesterol), which differs from cholesterol only by an extra double bond in the lateral chain. This sterol is the last precursor of cholesterol in one of its biosynthetic possible routes. However, in the liver desmosterol does not accumulate, despite high levels of cholesterol synthesis; in brain during maturation, however, large amounts of desmosterol are found as well as in human glial tumors? ,~ In recent experiments, large quantities of desmosterol were detected in brain tumors of the rat induced in our laboratories by nitrosourea derivatives according to Druckrey, et al? In ethylnitrosourea-induced oligodendrogliomas, desmosterol accounted for 10% to 15% of the total sterols. 12 Desmosterol was considerably higher in some neurinomas, which is not surprising since these tumors are quite malignant and fast-growing when compared with human neurinomas. The presence of consistent pools of desmosterol in brain tumors is connected with both the high sterol biosynthetic rate and with a blockade of desmosterol transformation into cholesterol. The ability of human brain tumors to synthesize both desmosterol and cholesterol from mevalonate was checked in vitro and compared with that of normal brain tissue. The results G indicate that the incorporation of mevalonate in the unsaponifiable lipid fraction is very low for the slow-growing neurinomas, which do not synthesize cholesterol, while the mest notable difference between glial tumors and normal brain is at the sterol level only. In fact, normal brain incorporated less radioactivity into sterols, and most of it was detected in cholesterol. The reverse was found in glial tumors, which showed a high sterol synthesis, and the ratio between synthesized desmosterol/cholesterol was higher in the glioblastomas than in other less malignant gliomas. Comparable results were obtained by incubating in vitro an experimental ependymoblastoma, which, after 1 hour of incubation, contained a twofold increase of radioactivity in desmosterol than in cholesterol. Desmosterol accumulation in brain tumors may be magnified by Triparanol administration. This drug, inhibiting desmosterol reductase, induces accumulation of desmosterol in blood but not in mature brain. This was demonstrated in mice with experimental